This invention relates generally to web guide apparatus and, more particularly, to an improved support and positioning system for such apparatus.
In numerous industrial and commercial processes, it is necessary that certain operations be performed upon a continuous travelling web of a thin material such as paper, plastic film or the like. In most such processes, it is necessary that the travelling web be maintained in proper registry with a machine that operates on the web. On occasion, however, the web becomes laterally misaligned relative to the machine. It is desirable that any such misalignment of the web be corrected as promptly as possible to avoid web wastage. A web guide apparatus which senses the lateral position of the web and automatically adjusts the web when it deviates from a desired position is commonly used for this purpose.
A typical web guide apparatus includes a stationary support frame which is attached to a floor or machine structure. A movable steering frame is mounted on the support frame. The steering frame includes a pair of spaced, parallel steering rollers over which the web is run. A sensor senses the lateral position of the web as it leaves the steering rollers and generates a signal to control a steering frame positioning device such as a motor or hydraulic cylinder. The motor pivots the steering frame relative to the support frame about a virtual pivot point along the center line axis of the incoming web to steer the web and reposition it laterally.
Various different systems have been utilized in web guide apparatus to support the steering frame for pivotal movement relative to the stationary support frame. Ideally, the support system should prevent rectilinear movement of the steering frame relative to the support frame and allow angular movement thereof only about a pivot axis perpendicular to the plane of travel of the web. Many prior support systems are simply ineffective in providing such single-degree-of-freedom motion, particularly with relatively large width webs which are under considerable tension.
For example, precision arcuate bearings of the type described in U.S. Pat. No. 3,390,823 are often used to support the steering frame. These bearings include arcuate guide bars which are mounted on the stationary support frame and constructed and arranged so as to have a common arc center at a point on the desired pivot axis. Curvilinear followers are slidably received on each of the arcuate guide bars and fixed to the steering frame for movement about the arc center. Unfortunately, in order to provide the desired single degree of freedom motion, such parts must be precision-machined and accurately oriented and mounted to the support structure and steering frame. They thus add considerably to the cost and complexity of the web guide apparatus. Multiple flexure frame supports of the type shown in U.S. Pat. No. 3,615,048 are equally complex and expensive, as are the link support structures found in U.S. Pat. No. 3,373,288.